Control valves are widely used to apply high pressure fluid, hydraulic or pneumatic, to one or more conduits connected to remote or local loads, and thereafter exhaust that fluid from the load. In three-way valves, the fluid is alternately supplied to and exhausted from a single load conduit; in four-way valves, the fluid is supplied to one load line as it is exhausted from another load conduit, and thereafter the fluid is exhausted from the first conduit and supplied to the second conduit. Such valves have many uses, but a primary use is as a directional control valve which supplies and exhausts fluid to and from each end of a cylinder to drive a piston. As high pressure fluid is applied to one end of the cylinder, it is exhausted from the other to drive the piston in a first direction. Thereafter, the high pressure fluid is supplied to the second end of the cylinder and exhausted from the first to drive the piston in the opposite direction.
Large three and four-way control valves are themselves generally controlled by one or more pilot valves. The pilot valves may be actuated manually, by a fluid, by a solenoid, or by any other drive mechanism.
One form of pilot operated four-way valve is shown in my prior U.S. Pat. No. 4,169,490. The valve shown in that patent includes four poppet valves which are driven pneumatically through respective diaphragms. The control pressures applied to the diaphragms can be obtained from a relatively simple pilot valve because a single pressure can be applied to each of the four diaphragms. The reverse operation of the valves required to close waste valves while supply valves are open and vice versa can be obtained by the mechanical arrangement of the poppet valves themselves. A disadvantage of poppet valves is that the poppets add to the expense of the system. Further, their large mass, relative to diaphragm valves, results in harder pounding of the poppet valves and thus increased wear. Therefore, in many applications a more simple and smaller mass diaphragm valve may be preferred despite the more complicated controls required for such systems.
One form of four-way valve in which the main valve members are diaphragms is shown in U.S. Pat. No. 2,911,005 to Adelson. In that system, a pilot valve alternately applies high and low control pressures to the back, control faces of one pair of diaphragms. A second valve responds to that control pressure to supply a reversed, low or high, pressure to the control faces of another pair of diaphragms. A significant disadvantage of the Adelson system is that it requires two different externally supplied levels of pressure, both of which are above the pressure level of the supply fluid to the main valve.
Another form of four-way valve wherein the main valving elements are diaphragms is shown in U.S. Pat. No. 3,016,918 to Wentworth. The Wentworth valve utilizes the pressure of the supply fluid to derive the control pressures to be applied behind the diaphragm valves. A disadvantage of the Wentworth and similar systems is that they require several flow restrictions in the control lines. Where the supply fluid contains foreign materials such as sand, grit, gums or varnish, which is the general case in industrial applications, those restrictions are subject to clogging. If filter elements are used to clean the supply fluid applied to the control network, those filters must be replaced or cleaned periodically.
Yet another form of pilot operated four-way valve wherein diaphragms are used as the main valving elements is shown in U.S. Pat. No. 2,984,257 to McCormick et al. In that system the control pressures are also derived from the supply fluid. Restrictions in the control network are avoided by the use of two separate but similar pilot valves. The pilot valves have to be operated by two separate, independent solenoids or by two other separate and distinct externally applied forces. The requirement for two actuators adds to the cost of the system, to the complexity of the system and to maintenance requirements. It is therefore advantageous, even where the system is solenoid actuated, to use only one solenoid or other actuator to actuate a single pilot valve.
Yet another form of piloted four-way control valve utilizing diaphragms as the main valve elements is shown in U.S. Pat. No. 4,385,639 to Holborow and U.S. Pat. No. Re. 29,481 to Larner. In those systems, the control pressures are obtained from pilot spool valves. The high control pressures are derived from the supply fluid. Sliding parts of spool valves require clean fluid because they are prone to "spool sticking" or "slide sticking" due to the effects of contaminants such as varnish and fine particulate matter. If filters are used, they must be replaced or cleaned periodically.